In prior art unit fuel pump-injectors, such as disclosed in U.S. Pat. No. 3,006,556 issued to Shade et al on Oct. 31, 1961, it has been conventional to provide a single elongated sleeve-type nut which substantially encloses a stacked plurality of both injector and pump components. The nut is threadably mated and tightened to a housing in order to retain the substantially enclosed components against separation and thereby join the respective abutting high pressure sealing end surfaces of these internal components.
A number of problems are encountered with this typical unit fuel pump-injector configuration. First, a relatively large number of internal components, such as a spray tip, spring cage, spring retainer, and fuel pump cylinder, are stacked and clamped between the single nut and the housing. Thus, the chances of successfully assembling the pump-injector and tightening the nut, without undesirably binding the reciprocable plunger in the pump cylinder, are very sensitive to the quality of surface finish and parallelism of each of the numerous abutting high pressure sealing end surfaces of the components.
Even if the required quality of surface finish and parallelism is achieved during manufacture of the components, the problem of the plunger binding in the pump cylinder can arise in attempting to reassemble a used and worn pump-injector that had been disassembled for cleaning or rebuilding. In such cases, the nut must be loosened or removed and the internal components must be shifted around several times or even relapped at their end surfaces before the nut can be properly tightened.
Second, the amount of high pressure fuel leakage between the internal components is also very sensitive to the quality of surface finish and parallelism of the numerous abutting sealing end surfaces of those parts. Excessive fuel leakage erodes and thereby irreparably damages the sealing end surfaces and also helps cause undesirably large tolerances on injector fuel flow rate and injector valve opening pressure.
Third, the entire pump-injector must be disassembled for servicing or rebuilding even though it is usually only the spray tip of the injector assembly that requires replacement or cleaning since only the spray tip is directly exposed to the severe environment of the engine combustion chamber. The combustion byproducts build up carbon and corrosive elements in the seat area between the spray tip and nut, in addition to the spray tip orifices, making it difficult to disassemble and clean the spray tip and nut. Conversely, the injector assembly of the pump-injector must be disassembled even though it may be only the pump assembly that requires servicing.
Fourth, evaluation and quality control of performance parameters such as fuel injector flow rate, fuel internal leakage rate, and injector valve opening pressure of the pump-injector is time consuming since the entire pump-injector must be carefully assembled, bench tested, and then completely disassembled in order to substitute injector spring shims or other internal components which will bring the parameters within acceptable tolerances.
In U.S. Pat. No. 2,560,799 issued to Johnson on July 17, 1951 there is disclosed a capsule which contains an injection valve and nozzle assembly to permit the assembly to be bench tested and observed in observation without connecting it to an engine. However, these teachings have never been adapted or applied to an injector assembly of a unit fuel pump-injector.
The present invention is directed to overcoming one or more of the problems as set forth above.